[Bugfix] Refactoring & Model path & attribute handling

Hi Aleksey,

install script: If you delete these entries ("eav_attribute"), all images respectively all category image paths would be deleted. So we changed it to your new model, before we recognized that the installscript isn't needed, because all instances of "Mage::getModel('catalog/category_attribute_backend_image')" are already instances of your new model.

model movement: Your model name didn't match model path. So we moved it on the right place.

refactoring (@see & model-node): We may not use CamelCase at this point.

best regards,

steven